Thread tension regulator for sewing machines



Jan. 4, 1955 R. GARBE THREAD TENSION REGULATOR FOR SEWING MACHINES Filed NOV. 7, 1951 2 Shets-Sheet l I N V EN TOR. c laua o lfgavbe BY WITNESS ATTORNEY" Jan. 4, 1955 GARBE THREAD TENSION REGULATOR FOR SEWING MACHINES Filed Nov. 7, 1951 2 Sheets-Sheet 2 INVENTOR. d udolf ga'rbe ATTORNEY WITNESS United States Patent THREAD TENSION REGULATOR FOR SEWING MACHINES Rudolf Gar-be, Rorschach, Switzerland, assignor to The Singer Manufacturing Company, Elizabeth, N. 1., a corporation of New Jersey Application November 7, 1951, Serial No. 255,154 11 Claims. (Cl. 112--254) The present invention relates to sewing machines and has for its primary object to improve the quality of the stitching at different speeds of operation of the machine. More specifically. the invention aims to provide means which will be effective throughout the range of from slow to high speed stitching to effect uniform concatenation of the stitching thread or threads within the body of the material being sewed.

The invention consists in the provision of speed responsive means for automatically varying the tension of a stitching thread and several embodiments of the invention are illustrated in the accompanying drawings, in which:

Fig. l is a front elevation view of a sewing machine having a thread regulator made in accordance with the present invention incorporated therein.

Fig. 2 is a fragmentary section view taken substantially on the line 22 of Fig. 1.

Fig. 3 is a section view of a work piece at a seam line and showing a seam produced by a sewing machine modified in accordance with the present invention.

Fig. 4 is a view similar to Fig. 3 but showing a seam produced by a sewing machine not equipped with the thread tension of the present invention.

Figs. 5 and 6 are schematic views of modified forms speed responsive, thread tension regulators. Although the present invention is capable of use with a chain-stitch sewing machine, it is especially adapted for use with a lock-stitch sewing machine.

The optimum thread tension imposed upon the upper thread of a lock-stitch type sewing machine is such as to produce a stitch in which the concatenation of the upper and lower threads is set at the midway point between the upper and lower faces of the work pieces, which may consist of one or more plies of material to be sewed. Such a seam is illustrated in Fig. 3 in which two uniform plies of work-pieces 10 and 11 have been sewed together by an upper or needle-thread 12 and a lower or bobbin-thread 13. It will be noted that the concatenations 14 of the threads 12 and 13 all lie substantially at the meeting faces between the plies of work pieces 10 and I1.

In Fig. 4, there is illustrated a seam that secures together the two uniform plies of work-pieces 10a and 11a and consists of a needle-thread 12a and a bobbin-thread 13a. In this figure, the concatenations of the threads are not uniformly located at the center of the work pieces but vary from the concatenation 14a at the left of the figure in which the bobbin-thread 13a is pulled completely through the work pieces to the concatenation 14 at the right in which the needle-thread 12a is pulled completely through the work pieces.

As is well known in the sewing art, it the upper thread tension is too great, the bobbin-thread will be pulled through the work-pieces, such as shown at 14a, and if the upper thread tension is too little, the needlethread will be pulled through the work pieces, such as shown at 141'. In the ordinary sewing machine, the upper thread tension can be varied by a trial and error method between the extreme limits which produce the concatenations 14a and 14 until the optimum setting is reached, i. e., that which will produce the concatenation 14e or 14f.

However, it has been found that the tension necessary to secure the optimum stitch setting may vary at different speeds of operation of the machine. Thus, a ma- .Thus, the tension 28 could be primary,

chine in which the thread tension has been properly set for a given sewing speed, may not sew properly if operated at a different speed, and the machine, consequently, can be adjusted accurately only for a single sewing speed. This condition is illustrated in Fig. 4 for one particular machine set for normal sewing speed, with the concatenations 14a, 14b and indicating relatively slow sewing and the concatenations 14h, 141 and 14j indicating relatively fast sewing. In view of the ability of the present day sewing machines to sew at extremely high speeds, and the necessity of versatility, improper sewing at any speed within its range of operation becomes a very serious drawback.

Due to the individual sewing characteristics of each type of sewing machine, the particular adjustment needed to correct the imperfections in the seam formation due to the varying speeds may be either an increase or a decrease in the upper thread tension. At present, due to the immense numbers of factors which determine the individual sewing characteristics, the adjustment necessary is determined by a trial-and-error method. In the following disclosure, the illustrated embodiments of the invention relate to a machine in which the tension is increased as the sewing speed is increased. However, it is to be understood that the present invention is also intended to include those machines in which the tension is decreased as the speed is increased, the distinction between the structural embodiments of the invention required for each being a mere mechanical expedient.

With reference to Fig. 1, the machine therein illustrated includes a base 20, the upper surface of which constitutes the work-support of the machine, and from the one end of which rises a standard 21 carrying the usual bracket-arm 22 overhanging the work-support and terminating in a head 23. The machine includes conventional sewing instrumentalities (for the most part not shown since they form no part of the present invention) including a needle 24a and a needle-actuating bracketarm or main shaft 24 bushing 25 carried by bracket-arm.

The tension means for the upper thread is herein shown as including a primary tension 27 and a secondary tension 28. The primary tension 27 is of any conventional construction and is adapted to place a constant drag upon the thread passing therethrough. The secondary tension 28 is the speed-responsive tension means that constitutes the present invention. Although the presently described preferred embodiment of my invention includes a primary and secondary tension means, it should be clear that only the secondary tension 28 could sufiice. or only prejournaled at one end in a bearing a transverse web or nb 26 in the liminary, or the sole tension means.

As illustrated in Figs. 1 and 2, the tension 28 is varied in accordance with the speed of the machine by a centrifugally actuated means including a collar 29 secured to the shaft 24 as by a set screw 30 and having springblades 31 secured thereto as by screws 32. Carried intermediate the ends of the spring-blades 31 and secured thereto as by rivets 33, are weights 34. The ends of the spring-blades 31 opposite the collar 29 are secured, as by screws 35, to a collar 36 loose on the shaft 24. A circumferential groove 37 formed in the outer surface of the collar 36 is adapted to' receive a roller 38 fitted upon a short arm 39 of a bell-crank lever 40 pivoted upon a pin 41 carried by a plug 42 screwed into the side wall of the bracket-arm 22. The bell-crank lever 40 also includes a long arm 43 that engages the inner end of a pin 44 extending into a hollow, partially split stud 45 mounted in a boss in the wall of the bracket-arm 20 and secured in the desired position by a screw 46. Externally of the bracket-arm 20, the pin 44 bears against a yoke 47, which in turn bears against the innermost one 48 of a pair of tension discs. A spring 49 is interposed between the outer tension disc 50 and air abutment plate 51 held onto the end of the stud 45 by an adjustable screw 52.

As will beclearly evident from the foregoing disclosure, rotation of the shaft 24 causes the weights 34 to fly outwardly to an extent dependent upon the speed of rotation of the shaft, thereby flexing the spring-blades 31 outwardly to draw the collar 36 towards the collar 29. The consequent rocking of the bell-crank lever 40 about its pivot 41 causes thearm 43 to bear against the pin 44 in a direction to increase the pressure between the tension discs 48 and 50. As the sewing speed decreases, the parts, of course, operate in the reverse to reduce the pressure between the tension discs.

In Fig. an electromagnetic means is employed to increase the thread tension according to the increase in the sewing speed. A shaft 24a corresponding to the shaft 24 in Figs. 1 and 2, has secured thereto an armature including a permanent magnet 60 disposed between two pole-pieces 61 carrying field windings 62 electrically connected to leads 74 of a circuit that includes a coil 63 surrounding an endwise offset soft iron core 64 carrying a pin 65 which extends through a stud 66 fitted in an aperture in the side wall of a bracket-arm 22a. Entered by the pin 65 are two cooperating tension discs 48a and 50a biased together by a coil spring 67 which surrounds the pin 65. A stop-plate 68 backed by an adjustable nut 69 holds the tension discs and the spring on the pin.

The generator in Fig. 5 produces alternating current. If it were desired to use direct current, an arrangement such as shown in Fig. 6 could be employed in which there is shown a D. C. generator comprising a permanent magnet field 70 surrounding an armature mounted on the shaft 24a and provided with three field windings '71 and three commutator segments 72. Brushes '73 wipe against the commutator segments and are electrically connected to the leads 74 which, as in the modification shown in Fig. 5, are in a circuit with the coil 63.

The operation of the modifications set forth in Figs. 5 and 6 are functionally the same as that set forth in Figs. 1 and 2. In accordance with the speed of rotation of the shaft 24a, and consequently, the sewing speed, there is a voltage generated directly proportional to the speed of rotation of the shaft, which energizes the coil 63 and which, in turn, effects endwise movement of the offset core 64 and its attached pin 65. As the pin 65 is urged inwardly against the resistance of the spring 67, the pressure between the tension discs 43a and 56a is accordingly increased. As the sewing speed is increased, the voltage generated and the thread tension are increased. Conversely, as the sewing speed is decreased, the voltage generated and the tension are decreased.

With an understanding of the present invention, it will be obvious to those skilled in the art that the specific structural details of the tension means form no part of the present invention.

Numerous other alterations of the structure herein disclosed will suggest themselves to those skilled in the art. However, it is to be understood that this disclosure relates to the presently preferred embodiments of my invention which are for purposes of illustration only and not to be construed as limitations of my invention. All such medi fications which do not depart from the spirit of my inven tion are intended to be included Within the scope of the appended claims.

Having thus set forth the nature of the invention, what I claim herein is:

1. Means for automatically adjusting the thread tension in a sewing machine in response to variations in the sewing speed thereof, comprising an adjustable threadtension device having an adjusting element, sewing speed responsive control means carried by said sewing machine, and operative connections between said control means and said adjusting element of said thread-tension device.

2. A sewing machine having a primary and a secondary needle-thread tension-device, one of said tensiondevices being variable, control means associated with said sewing machine and responsive in its effective action to the sewing speed thereof, and operative connections between said control means and said variable threadtension devices to vary the drag thereby imposed upon a thread in response to the sewing speed of the machine.

3. In a sewing machine having instrumentalities operable to perform a sewing operation with a stitching thread. a variable tension device for imposing a drag upon the stitching thread during operation of said instrumentalities, automatic control means responsive to the sewing speed of said instrumentalities, and operative connections between said control means and said tension device for automatically varying the magnitude of the drag imposed upon the thread by said tension device in accordance with the variations in the sewing speed of said instrumentalities.

4. In a sewing machine having a stitching mechanism operable to produce a lock-stitch seam including a needlethread, a variable tension device for imposing a drag upon the needle-thread during operation of said stitching mechanism, speed-responsive control means operatively associated with said stitching mechanism to respond to variations in the sewing speed of said stitching mechanism, and operative connections between said control means and said tension device for automatically varying the magnitude of the drag imposed upon the thread by said tension device in accordance with the variations in the sewing speed of said stitching mechanism.

5. In a sewing machine having a stitching mechanism operable to perform a sewing operation with a stitching thread, a variable tension device for imposing a drag upon the stitching thread during operation of said stitching mechanism, said tension device including an actuating element for varying the drag thereby imposed upon the stitching thread, automatic control means responsive to the sewing speed of said stitching mechanism, and operative connections between said control means and the actuating element of said tension device for automatically varying the magnitude of the drag imposed upon the thread by said tension device in accordance with the variations in the sewing speed of said stitching mechanism.

6. In a lock-stitch sewing machine .having a rotating needle-actuating shaft and a variable needle-thread tension device, said tension device including an actuating pin for varying the magnitude of the drag thereby imposed on the needle-thread when the pin is moved relative to said tension device, and a speed responsive means operatively connected to said shaft and said pin to automatically shift the pin relative to said tension device in accordance with variations in the speed of rotation of said shaft.

7. In a lock-stitch sewing machine having a rotating needle-actuating shaft and a variable needle-thread tension device, said tension device including an actuating pin for varying the magnitude of the drag thereby imposed on the needle-thread when the pin is moved relative to said tension device, and a speed responsive means operatively connected to said shaft and said pin to automatically shift the pin relative to said tension device in accordance with variations in the speed of rotation of said shaft, said speed responsive means comprising a flyweight carried by said shart for rotation therewith and adapted to be swung outwardly with respect to said shaft by centrifugal force, a collar loosely mounted upon said shaft for movement lengthwise thereof by the swinging of said :iyweight, and operative connections between said collar and said pin.

8. In a lock-stitch sewing machine having a rotating needle-actuating shaft and a variable needle-thread tension device, said tension device including an actuating pin for varying the magnitude of the drag thereby imposed on the needle-thread when the pin is moved relative to said tension device, and a speedresponsive means operatively connected to said shaft and said pin toautomatically shift the pin relative to said tension device in accordance with variations in the speed of rotation of said shaft, said speed responsive means comprising an electric generator associated with said shaft, a solenoid associated with said pin, and electrical connections between said generator and solenoid.

9. In a lock-sttich sewing machine having a bracketarm, a rotating needle-driving shaft journaled internally of the bracket-arm, a variable needle-thread tension device secured externally of said bracket-arm, said needlethread tension device including a pin extending through an aperture in the side wall of said arm and at its outer end operatively engaging the tension device for varying the magnitude of the drag thereby imposed on the needlethread when said pin is moved relative to the side wall of the bracket-arm, and a speed responsive means associated with said shaft and with the inner end of said pin to automatically shift said pin relative to said side wall upon variations in the sewing speed.

10. In a sewing machine having a stitching mechanism including a threaded needle and a complemental looptaker adapted to be actuated through a stitching cycle to form a lock-stitch, said cycle including the step of the stitch-setting, a variable needle-thread tension device for 1mpo s1ng a drag upon the needle-thread during operation of said stitching mechanism, automatic control means responsive to the sewing speed of said stitching mechanism, and operative connections between said control means and said tension device for automatically varying the drag imposed upon the needle-thread during stitch setting by said tension device in accordance with the variations in the sewing speed of said stitching mechanism.

11. In a sewing machine having a stitching mechanism operable to produce a lock-stitch seam including a needlethread, a variable tension device for imposing a drag upon the needle-thread during operation of said stitching mechanism, said tension device comprising a pair of relatively movable elements for clamping the needlethread therebetween and a resilient bias for urging one of said elements into engagement with the other, speed-responsive control means operatively associated with said stitching mechanism to respond to variations in the sewing References Cited in the file of this patent UNITED STATES PATENTS 2,128,033 Zonis Aug. 23, 1938 FOREIGN PATENTS 216,963 Great Britain June 12, 1921 225,541 Germany May 1, 1943 

